Chemical oxygen generators of this type are used as an alternative to oxygen pressure tanks in emergency oxygen devices installed on board of civil aircraft mainly. These emergency oxygen devices serve to supply oxygen to passenger or cabin crew in case of an emergency situation like a decompression situation. In such a situation an oxygen flow is provided to an oxygen mask which can be worn by the passenger in order to allow him constant breathing and sufficient uptake of oxygen for his vital functions.
It is known in the prior art to include a chemical oxygen generator in such an emergency oxygen device as a source of oxygen. Such chemical oxygen generators include a solid material serving as the oxygen source such as sodium chlorate which can produce oxygen in a chemical reaction with iron. This chemical reaction is started in case of an emergency situation, e.g. by the passenger pulling the mask to himself and thus actuating a respective switch whereby a pyrolytic reaction is started in a pyrolytic ignition unit effecting local heating of the solid material in a starting region. In this starting region, the chemical reaction begins which is exothermic and thus causes the solid material to continuously react in a chemical reaction and produce oxygen in a gaseous state.
A first problem associated with such emergency oxygen devices utilizing a chemical oxygen generator is the procedure of starting the chemical reaction which requires a specific interaction of mechanical and pyrolytic components. This interaction is prone to misuse and maloperation and can not be adapted to modern cabin control systems with regard to maintenance and safety conditions.
A second problem associated with such emergency oxygen devices utilizing chemical oxygen generators is the non-constant production of oxygen as a result of the chemical reaction. Generally, a delayed production of oxygen occurs after ignition and initial start of the chemical reaction. Hereafter, in a first phase of the chemical reaction, only a small volume of oxygen is produced which is in particular unfavorable because the aircraft may at this time be in high altitude flight level wherein a decompression situation within the cabin requires a high amount of oxygen to be supplied to the passengers to maintain their vital functions. Hereafter, in a later stage of the chemical reaction, a large volume of oxygen is produced because the chemical reaction is fully activated in the solid material. However, in this second stage the aircraft may have descended to a low altitude flight level in order to relieve the decompression situation and the passenger may only require a small amount of oxygen at this flight level. However, given a situation where the decompression situation occurs in a long distance to the nearest suitable airport, the aircraft may expect a long flight time until it reaches the airport and thus it would be ideal to supply a small amount of oxygen over a long time to the passenger. It is an object of the invention to improve the delivery rate of oxygen by an emergency oxygen system with regard to these conditions.
In a first approach, it is known in the prior art to include an oxygen pressure tank in an emergency oxygen device storing oxygen in a pressurized state. Using such pressurized oxygen it is possible to immediately supply a large amount of oxygen to the passenger in an emergency situation and to reduce this supply by a respective control valve in a later stage of the continuing emergency situation when flying at low altitude flight level. It is further known to combine such an oxygen pressure tank with a chemical oxygen generator in an emergency oxygen device to allow immediate supply of oxygen out of the pressure tank in the first stage of the emergency situation and to provide oxygen for a long time out of the chemical oxygen generator in a later stage. However, a major draw back of these systems is the need to handle high pressures within the emergency oxygen system with requires continuous safety checks and maintenance of the system to ensure proper function of the system. Further, such oxygen pressure tanks must be completely sealed in order to hold the required amount of oxygen inside and a leakage of oxygen out of such tanks is very dangerous in that the air inside the aircraft may be enriched with oxygen and thus the risk of fire on board the aircraft is increased. A further draw back of such systems is the significant weight of such a pressure tank which is caused by the wall thickness required for bearing the high inner pressure inside the tank.
Generally, the oxygen flow out of a chemical oxygen generator may be regulated using a control valve to compensate for some of the problems associated with such chemical oxygen generators. However, this causes significant disadvantages in the system. First, by throttling the oxygen flow the pressure inside the chemical oxygen generator will significantly increase and this requires the housing of the oxygen generator to be configured to take up such inner pressure. By this, a significant advantage of chemical oxygen generators, namely its low weight, is sacrificed. Secondly, such increase of pressure inside the chemical oxygen generator will inadvertently influence the chemical reaction and may result in a reduction of the reaction. This, however, makes its difficult to control the oxygen flow and in particular produces the risk that the chemical reaction is stopped or reduced to a degree which is not sufficient for the production of enough oxygen for the passenger.